The Chancellor's helicopter flight to HMS Kent, a type 23 frigate, and a meeting with sailors' families was billed as part of the nationwide tour he announced at Labour's 2005 conference. But there was little doubt that the appearance represented the latest choreographed step on the long road to No 10 for Mr Brown.

As Tony Blair prepared to fly to Berlin last night for talks with Angela Merkel, the German Chancellor, Mr Brown also briefed the Cabinet on the spending round to come and announced that the date for his 10th Budget - and possibly his last - would be 22 March.

Meanwhile, his close friend, Alistair Darling, the Transport Secretary, cleared the way for the succession without a challenge. Mr Darling, who is likely to have a senior post in a Brown Cabinet, said Mr Brown was the "natural successor" to Mr Blair and is likely to become the next leader without a contest from any cabinet colleague.

Left-wingers such as Michael Meacher, the former environment minister, are likely to force a contest to offer an alternative agenda. Mr Brown's allies say he will relish the challenge.

"I don't see any senior colleagues standing against him," Mr Darling said in the London Evening Standard. "I think the mood generally in the Labour Party is that, when Tony decides to step down, Gordon is the natural successor and he will take on the work that Tony started. I think Gordon will be the next leader."

John Reid, the Defence Secretary, has also cleared the way for Mr Brown to take the leadership without a cabinet challenger. Burying old antagonisms with the Chancellor, the Defence Secretary said he believed Mr Brown was committed to the reforming agenda introduced by Mr Blair.

"I have never been prepared to sponsor anyone other than the present leader while we have Tony Blair there," he said in the Financial Times. "But I am equally certain that whoever takes over from him - including Gordon Brown - will be as committed to reform and renewal as Tony Blair is."

Mr Brown was blamed for Labour's humiliating defeat last Thursday in the Dunfermline and West Fife by-election, the seat in which he now lives with his wife, Sarah, and son, John, after boundary changes. Sir Menzies Campbell, the acting Liberal Democrat leader, said that if Mr Brown could not win in his own backyard, how would he win in Surrey.

However, Mr Brown has ended the week looking unassailable. He backed Mr Blair in the BBC's Andrew Marr programme on Sunday over ID cards, helping the Prime Minister to survive a rebellion in the Commons on Monday. He also came to Mr Blair's aid on Monday with a speech to the Royal United Services Institute, strongly supporting radical measures against terrorism, including returning in future to 90-day detention without trial for terrorist suspects.

He voted with Mr Blair on Tuesday for a total ban on smoking, leaving his ally John Prescott, the Deputy Prime Minister, to go into the opposite division lobby in a rare split between the two men. His support on terrorism helped destroy a revolt against the Terrorism Bill on Wednesday.

Ironically, the ease with which Mr Blair overcame the threats to his authority in the Commons shored up the Prime Minister's authority, and potentially delayed the day when Mr Brown might finally seize the crown.

In the meantime, he is being schooled by Mr Blair's own advisers - Alastair Campbell, Mr Blair's former communications director, and his polling guru, Lord Gould - on widening his electoral appeal to overcome the threat of David Cameron, who is busy wooing Middle England. Mr Brown's allies deny they have been doing a "makeover" on the Chancellor's image as the dour Scotsman from the manse.

But there is no doubt that he has set about softening the "Iron Chancellor" image. His trips to Africa and Israel helped to show a commitment to fighting poverty and a series of speeches have allowed him to escape the straitjacket of the Treasury.

A friendly interview in the Daily Mirror this month featured photographs of his son, and he talked about how much fatherhood had changed him. He made a speech on "Britishness" for which he was accused of wrapping himself in the Union flag.

Yesterday, Mr Brown told naval officers: "It's very important to reward the dedicated service of our armed forces. Today's settlement of 3 per cent, and 3.3 per cent for the junior ranks, is higher than other settlements will be. We must recognise the contribution of our armed forces and give recognition and encouragement for more people to join up."

The choreography of succession?

* 4 January Gordon Brown begins to expand his role, setting out plans to help children of the world "break free from the vicious cycle of illiteracy, unemployment and poverty".

* 14 January In a speech on "Britishness", he bursts out of the Treasury straitjacket to call for Britain to celebrate the Union Flag. Advisers concede it sounds "too American" and risks being outflanked by David Cameron, saying "the British don't do flags"

* 16 January Sarah, his wife, announces she is pregnant. The Chancellor underlines his credentials as a family man - which will come in useful if he runs against father-of-three David Cameron at the election.

* 24 January He uses an interview in The Sun to win over rebel MPs to back the controversial schools reforms, on which the Prime Minister's authority could be wrecked.

* 6 February Says that the birth of his son John two years ago helped him realise "there are things far more important in life than politics". The photoshoot shows Gordon and Sarah in front of John's toys.

* 7 February Uses a BBC interview en route to Birmingham to throw his weight behind the controversial Bill to make "glorification" of terrorism an offence. It follows the conviction of Abu Hamza and outrage at the failure of the police to arrest Muslims who protested with placards calling for the beheading of those who offend their faith.

* 9 February Suffers blow to authority after Labour defeat in the Dunfermline and West Fife by-election in his backyard. Sir Menzies Campbell says if he cannot win in Fife, he cannot win in Surrey, raising questions over his ability to lead Labour.

* 12 February Denies that he and Tony Blair are operating a "dual premiership" and supports ID cards. He is later described as speaking with "prime ministerial style".

* 13 February Gives most outspoken support for the war on terror, claiming three attacks had been thwarted. Also announces "National Veterans' Day" on 27 June. Aides deny he is being given a "makeover" by Alastair Campbell and Lord Gould.

* 16 February Flies to HMS Kent to announce the 3 per cent pay rise for the armed forces. Kofi Annan says he has asked Mr Brown to join a panel of advisers to review the UN's handling of humanitarian assistance and the environment. Mr Brown also announces the date of his next (final?) Budget, 22 March.

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